In the drilling of an oil and/or gas well, a specially formulated fluid known as “drilling mud” is circulated through the wellbore. During rotary drilling operations, the drilling mud serves multiple functions, including protecting against blowouts by holding back subsurface pressures of formation fluids. As long as the bore hole contains a sufficient volume of drilling mud of a sufficient density, the pressure created by the weight of the column of drilling mud is typically sufficient to prevent formation fluids from entering the bore hole. If a formation having higher pressure than expected is encountered during drilling operations, however, the potential for formation fluids, including gas, to enter the borehole and migrate toward the surface is present.
When formation fluids enter the bore hole, a pressure spike, or “kick” as they are commonly referred to in the industry, can occur. Ram-type BOPs are part of a pressure control system used in oil and gas drilling operations to control these unexpected well bore pressure “kicks.” The BOPs are designed to close off the well to prevent a blowout by sealing the well against the fluid pressure from below. By sealing the well, the BOP prevents gas (and other well fluids) from migrating past the BOP stack to the drill floor of a rig where numerous potential ignition sources exist that could ignite the gas and thereby cause a blowout. A BOP can also be used to seal off the well around the drill string in normal drilling operations involving positive downhole pressure.
BOPs are typically included in the surface assembly at a wellhead when drilling or completing a well. Typically, multiple BOP rams are assembled in a vertical stack that is positioned over and connected to the wellhead.
The BOP has a central valve body with a vertical bore running through it. Wellbore tubulars, such as the drill string or coiled tubing, extend up through the center, vertical bore of the BOP stack. Similarly, during wireline logging operations, wireline extends up through the center, vertical bore of the BOP stack. Depending on the operations being conducted on the well, other wellbore equipment may be within the vertical bore of the BOP stack at a particular time.
A typical BOP has a plurality of laterally disposed, opposing actuator assemblies fastened to the valve body. Each actuator assembly includes a piston that is laterally moveable within an actuator body by pressurized hydraulic fluid (during normal operation) or by manual force (in the event of a failure of the hydraulic control system). Each piston has a stem threadably engaged or otherwise connected to it. The stem extends laterally toward the bore of the valve body and has a ram body attached to the end of the stem nearest the bore of the valve body.
Replaceable sealing elements are mounted within or on the ram bodies that extend into the vertical bore of the valve body of the BOP. When the pistons of the BOPs are moved to a closed position, commonly referred to as “closing the rams,” the vertical bore of the BOP is sealed and the well bore pressure is contained. The sealing elements mounted within or on the ram bodies are available in a variety of configurations designed to seal the vertical bore of the BOP valve body when the opposing rams and pistons are moved to their closed position.
Several types of ram and seal assemblies are used in the actuator assemblies of a BOP stack. One type of ram and seal assembly known as a “pipe ram” utilizes seals designed to seal around the wellbore tubulars within the BOP's vertical bore when the BOP is closed. Each seal of a pipe ram typically has a semicircular opening in its front face to form a seal around half of the outer periphery of the tubular. When the pipe rams are closed, the opposing pipe rams engage each other and seal the entire periphery of the tubular, thereby closing off the annulus between the tubular and the well bore surface.
Another type of ram and seal assembly, known as a “blind ram,” seals across the entire wellbore when no tubular is located in the vertical bore at the location of the blind rams. Like pipe rams, the blind rams are designed to engage each other when the BOP is closed. Blind rams, however, typically utilize seals with no opening in the face of the seals such that the blind rams form a complete seal through the vertical bore of the BOP.
BOP stacks typically also include shear, or cutting, rams that shear the tubular (or wireline) when the rams are driven toward each other as the BOP is closed. In operation, the shear rams are typically used as a last resort measure to contain wellbore pressure from causing a blowout. A BOP with shear rams is typically the top section of a ram-type BOP stack, while various pipe rams and blind rams are typically located below the shear rams. In operation, the pipe rams will be closed first to try to contain the wellbore pressure and prevent a potential blowout. In the event the pipe rams (and/or the blind rams) do not contain the “kick,” the shear rams are actuated to try and contain the “kick” and prevent a potential blowout.
The shear ram assemblies must be sealed to prevent wellbore fluids from migrating through or around the shear blades after the tubular or other item within the valve body of the BOP is sheared. Various prior art patents disclose shear rams with integral sealing means disposed on or within the shear blades and/or within the shear ram bodies. Such prior art patents include U.S. Pat. Nos. 4,580,626; 4,646,825; 6,244,336; and 6,719,042. Each of these patents energize the seal between the shear blades in different ways. However, the designs of the sealing mechanisms of each of these prior art patents have certain drawbacks that limit the amount of squeeze that may be placed on the seals and/or that make replacement of the sealing components difficult.
The present invention offers an improved sealing mechanism that “energizes” the sealing element between the shear blades in a unique way and that offers a design that allows for easy replacement of the seal assembly. Thus, the sealing mechanism of the present invention overcomes many of the drawbacks of the prior art.